1. Field of the Invention
The present invention relates generally to wipe pattern generators and, more particularly, to a wipe pattern generator in which data expressed by polar coordinates to indicate a shape of a wipe pattern is stored in a memory and a wipe pattern signal is generated based on the data thus stored in the memory.
2. Description of the Prior Art
An official gazette containing Japanese laid-open patent application No. 56-65575 discloses a special effect signal generating apparatus. According to this previously-proposed special effect signal generating apparatus, various patterns such as a circle, a diamond and so on are drawn on a monitor screen, and a video signal different from a video signal displayed on the outside of the drawn pattern is displayed on the inside thereof. The above prior-art special effect signal generating apparatus includes a wipe pattern generator in order to generate wipe patterns such as a circle, a diamond and the like.
In the prior-art wipe pattern generator, data indicating a vertical fundamental wipe pattern and data indicating a horizontal fundamental wipe pattern are stored in vertical and horizontal fundamental wipe pattern memories, respectively. When a wipe pattern signal is generated, the data indicating the vertical fundamental wipe pattern and the data indicating the horizontal fundamental wipe pattern are read out from the vertical and horizontal fundamental wipe pattern memories on the basis of vertical and horizontal synchronizing signals of a video signal. Then, the data thus read are compared with a fader level, following which they are mixed with each other and thereby generated as a wipe pattern signal.
In the prior-art wipe pattern generator, however, data used to form a wipe pattern are divided into vertical and horizontal directions data and are then stored in the memories as described above. This makes it difficult to generate a wipe pattern of a complex shape, to radially modulate a wipe pattern and to rotate a wipe pattern.